Which small intestine segment is primarily responsible for nutrient absorption?

The jejunum is the segment of the small intestine that is primarily responsible for nutrient absorption. It is located between the duodenum and the ileum and comprises the second part of the small intestine. The jejunum has a thicker wall, a greater vascular supply, and a more extensive surface area due to its numerous villi and microvilli, which enhance its ability to absorb nutrients effectively.

While the duodenum is also involved in digestion and nutrient absorption, particularly in the initial stages after food leaves the stomach, it primarily plays a role in the chemical digestion of food through enzymes and bile, rather than in the absorption of the majority of nutrients. The ileum is primarily responsible for absorbing bile acids and vitamin B12, although it can absorb some nutrients as well.

The ascending colon is part of the large intestine and primarily functions in the absorption of water and electrolytes, not in the absorption of nutrients from digested food. Therefore, the jejunum's specific anatomical features and its function align it as the main site for nutrient absorption within the small intestine.